The Ge\(V\)  complex is a neutral defect, being Ge isoelectronic to silicon, and, differently from conventional dopants, does not show hydrogen-like shallow states, but deep energy levels related to the dangling bonds
in the vacancy.
In the Ge\(V\)  ground state a deep level within the valence band and a defect state in the gap are filled by the four unpaired electrons from the dangling bonds.
Further electrons,
injected into the channel
by applying a small bias voltage between the source and the drain electrodes,
occupy strongly-bound
defect states in the energy gap, experiencing a relatively large on-site Coulomb repulsion (\(U\simeq 150\)  meV).
Depending on the amplitude of the inter-site hopping,
the channel may behave as a
more-or-less
strongly-correlated system, where the Mott-Hubbard physics applies [1]}, [2]}.
